1. Technical Field
The present disclosure relates to a lithium ion secondary battery and a method for manufacturing the same.
2. Related Art
A lithium ion secondary battery includes a power generating element including a stack of a positive electrode, a separator, and a negative electrode. The separator has a function of holding an electrolyte solution for securing the lithium ion conduction between the positive electrode and the negative electrode, and a function of preventing the short-circuiting between the positive electrode and the negative electrode. In order to achieve the functions, the separator is formed to be sufficiently large relative to a region opposite to the positive electrode and the negative electrode (hereinafter referred to as “opposite region”) (that is, the separator is formed to have a sufficient “surplus region”).
As the lithium ion secondary battery is used, the electrolyte solution held in the opposite region of the separator moves to the surplus region (i.e., the region not opposite to the positive electrode and/or the negative electrode). When the electrolyte solution has moved to the surplus region, the capacity of the lithium ion secondary battery is decreased. In order to avoid this decrease in capacity of the lithium ion secondary battery, the porosity of the surplus region is set smaller than the porosity of the opposite region (i.e., a region with low porosity (hereinafter referred to as “low-porosity region”) is formed in the surplus region) (see JP-A-2013-118057).